The subject matter of the present invention relates to an anchor apparatus adapted to be disposed in a wellbore and a method for releasing the anchor and dropping a perforating apparatus when a frangible member is shattered in response to a detonation wave propagating in a detonating cord, and more particularly, to an anchor apparatus and a method for propagating a detonation wave in a detonating cord, shattering a frangible member in response to the detonation wave, unsetting the anchor apparatus from a wall of the wellbore using a primary release mechanism when the frangible member shatters, unsetting the anchor apparatus using a secondary release mechanism when the primary release mechanism is not used, and, when the anchor apparatus is unset, dropping the perforating apparatus to a bottom of the wellbore.
In U.S. Pat. No. 5,293,940 automatic tubing release apparatus adapted to be disposed in a wellbore includes a frangible member and enclosed detonating cord. The frangible member shatters when a detonation wave, propagating in the detonating cord, passes through the frangible member. Before the frangible member shatters, a perforating apparatus is connected to a tubing. However, when the frangible member shatters, the perforating apparatus is automatically released from the tubing and the perforating apparatus falls to a bottom of the wellbore.
In U.S. Pat. No. 5,318,126, which is a continuation in part of the aforementioned U.S. Pat. No. 5,293,940, an explosively opened production valve adapted to be disposed in a wellbore includes the same frangible member with enclosed detonating cord adapted to conduct a detonation wave. The production valve is initially disposed in one state (e.g., a closed state). However, when the frangible member shatters in response to the detonation wave, conducting in the detonating cord, passing through the frangible member, the production valve changes from the one state to another state (e.g., an open state).
In U.S. Pat. No. 5,366,013, which is a continuation in part of the aforementioned U.S. Pat. No. 5,318,126, a shock absorber adapted to be disposed in a wellbore includes the same frangible member with enclosed detonating cord adapted to conduct a detonation wave. The shock absorber initially cannot absorb shock. However, when the frangible member shatters in response to the detonation wave passing through the frangible member, the shock absorber is then ready to absorb shock.
In all of the aforementioned applications, a detonating cord is enclosed by a frangible member. When a detonation wave propagates within the detonating cord, the detonation wave passes through the interior of the frangible member.
In response to the detonation wave, the frangible member shatters. When the frangible member shatters, an event occurs. For example, in the aforementioned patent, a perforating gun will be automatically released from a tubing, or a production valve will change state, or a shock absorber will be ready to absorb shock. However, none of the aforementioned applications disclose a novel anchor apparatus including the automatic release of the anchor when the frangible member shatters in response to the detonation wave passing through the frangible member.
U.S. Pat. No. 5,025,861 to Huber et al, and associated divisional U.S. Pat. Nos. 5,095,993 and 5,050,682, disclose an apparatus including a perforating gun and an anchor for anchoring the perforating gun to a casing prior to detonating the perforating gun. In these Huber et al patents, two interleaved coil springs having beveled shaped surfaces comprise the anchor. Compression of the inner coil spring forces a radial expansion of the outer coil spring. When the perforating gun detonates, the gun remains anchored to the casing. The anchor can be released by a slickline manual operation or by an automatic operation by high order detonation of the perforating gun. In the slickline manual operation, a separate shifting tool, connected to a shifting profile of the anchor, pulls upwardly on the fishing profile and releases the anchor from the casing. As a result, after the perforating gun detonates, a separate action is required to release the anchor from the casing. While this anchor is sufficient for some purposes, a novel monobore anchor is needed for monobore completion situations in a wellbore. The term "monobore completion" refers to a single diameter of casing and a single diameter of tubing throughout the entire length of a wellbore. The new monobore anchor would include a new anchor apparatus and a new redundant unsetting apparatus for unsetting the anchor. For example, a primary unsetting apparatus would automatically unset the anchor from the casing in response to a detonation wave propagating through a detonating cord on its way to the perforating gun. As a result, in order to unset the anchor, no separate action would be required by an operator, and the previously required overshot and fishing profile would not be needed.
U.S. Pat. No. 4,815,540 to Wallbillich III and U.S. Pat. No. 4,526,233 to Stout disclose an apparatus for releasing a perforating gun from a tubing. In both of these patents, the perforating gun is secured to the tubing by a latch mechanism. When the perforating gun discharges, the latch mechanism ultimately releases the gun from the tubing. In the Wallbillich patent, following detonation of the perforating gun, a ball must first fall to a seat and tubing pressure must be increased in order to effect release of the latch mechanism. In the Stout patent, following detonation of the perforating gun, gas pressure produced from detonation of the perforating gun must be relied upon to effect release of the latch mechanism and release of the perforating gun from the tubing. However, none of the aforementioned patents automatically release an anchor thereby releasing a perforating gun from a casing when a detonation wave, propagating in a detonating cord, shatters a frangible member and nearly simultaneously detonates the perforating gun.